Increased atherosclerotic lesions and Th17 in interleukin-18 deficient apolipoprotein E-knockout mice fed high-fat diet.

Recent reports show T helper 17 (Th17) cells are involved in the pathogenesis of various chronic inflammatory diseases formerly categorized as Th1-mediated disorders. Interleukin-18 (IL-18) induces Th1 cells to produce interferon-gamma (IFN-gamma) which is proatherogenic, while cholesterol causes atherosclerosis and stimulates intact rat aortae to produce prostaglandin E(2) (PGE(2)), a strong regulator of IL-23 that expands Th17. We wanted to test whether Th17 is proatherogenic and whether cholesterol can induce the alternative Th17 pathway in IL-18 deficient apolipoprotein E-knockout (ApoE(-/-)) mice that have reduced Th1 cells, if they are fed high-cholesterol diet. IL-18(+/+)ApoE(-/-) and IL-18(-/-)ApoE(-/-) mice aged 5 weeks were fed high-cholesterol diet (HCD) and control littermates of IL-18(-/-)ApoE(-/-) low-cholesterol diet (LCD) for 12 weeks. At termination, cryosectioned aortic arches were stained for lesion measurement and immunohistochemistry. We found that serum cholesterol and triglyceride levels were significantly higher in IL-18(-/-)ApoE(-/-) mice on HCD and they also had significantly increased atherosclerosis compared with 18(+/+)ApoE(-/-) mice or IL-18(-/-)ApoE(-/-) mice on LCD. Increased atherosclerosis correlates with enhanced Th17-cells, IL-23-producing vascular smooth muscle cells (VSMC) and macrophages, and thin fibrous cap in lesions, the morphology indicative of unstable plaques prone to rupture. In vitro, cholesterol significantly enhances VSMCs explanted from IL-18(-/-)ApoE(-/-) but not IL-18(+/+)ApoE(-/-) aorta to produce IL-23 and homocysteine mediates secretion. This study suggests that in IL-18 deficiency, cholesterol in HCD synergize mechanistically with homocysteine to accelerate atherosclerosis via the alternative IL-23/Th17 pathway, demonstrating a new role for Th17 in atherosclerosis.

Predominance of Th2 response in human abdominal aortic aneurysm: mistaken identity for IL-4-producing NK and NKT cells?

Abdominal aortic aneurysm (AAA) is a complex remodeling process that involves both synthesis and degradation of extracellular matrix proteins in the aortic wall, leading to decreased tensile strength, progressive dilation and eventual rupture. Chronic inflammation, increased local production of elastin-degrading proteases by inflammatory cells and destruction of medial elastic lamellae play important roles in aneurysm progression. Neovascularization in all layers of the arterial wall is prominent and angiogenesis can facilitate chronic inflammation. It is still unclear what initiates aneurysmal dilation and what determines its progression. The complex nature of the process has defied elucidation. Apart from macrophages, the predominant immune cell infiltrates reported so far are CD3(+)T cells that express CD4 and CD8. Infiltrates of type 2 Th cells and their production of IL-4 and IL-5 have been implicated in AAA development. However, NKT and NK cells have a Th0 cytokine profile and can also produce type 2 as well as type 1 (IL-2 and IFNgamma) cytokines. We have demonstrated the presence of NK and NKT cells in AAA tissue. With their growing importance in autoimmunity and transplantation, they may play a role in AAA development. Therefore, there is a need to use a combination of T and NK markers to fully characterize both innate and adaptive lymphoid cell subsets in local inflammatory infiltrates in order to elucidate their roles in AAA progression.

Atherosclerotic abdominal aortic aneurysm and the interaction between autologous human plaque-derived vascular smooth muscle cells, type 1 NKT, and helper T cells.

Immune cell infiltration, vascular smooth muscle cell (VSMC) proliferation, and apoptosis are pathological hallmarks of atherosclerosis. The multifocal, chronic, and inflammatory nature of this disease of the cardiovascular system complicates targeted cellular therapy and emphasizes the need to understand the role and interaction of immune cells with VSMCs. We characterized the immune cell subsets present in human atherosclerotic tissue derived from atherosclerotic abdominal aortic aneurysm (AAA) and expanded them to study their interaction with autologous plaque-derived VSMCs in vitro. We show here that apart from T lymphocytes, plaque infiltrates consist of lots of NK cells and significant proportions of NKT cells that express T cell receptor (TCR) alphabeta, CD4, and the NK markers CD56 and CD161. The infiltrates are predominantly IFN-gamma-producing Type 1 lymphoid cells. When cocultured, the T and NKT cells adhere to VSMCs. CD4+ T cells enhance VSMC proliferation. VSMCs in turn enhance CD4+CD161+ NKT but not CD4+ or CD8+ T cell proliferation. CD4+CD161+ NKT cells inhibit VSMC proliferation by inducing apoptosis. Our results suggest that the interactions of Type 1 CD4+ T and CD4+CD161+ NKT cells with VSMCs may regulate VSMC proliferation and death respectively in atherosclerosis and the balance of these interactions could determine plaque stability.

NKT cell subsets in infection and inflammation.

We recently identified two stably expressed cell surface markers, IL-18R and ST2L, which are selectively expressed on T1/NK1 and T2/NK2 cells, respectively. Here we use these molecules in direct ex vivo analysis of PBMCs from patients with AIDS, psoriasis (PS) atherosclerosis and to show the importance of these markers as determinants of the functional dichotomy of lymphocyte subsets, in particular NKT. In a cohort of 22 HIV patients made up of a mixture of long term non-progressors, seroconvertors, progressors and asymptomatics, we found a clear NKT1 to NKT2 shift (P=0.001) in the HIV-infected individuals. We also show a predominance of NKT2 cells over NKT1 cells in the PBMCs of patients with mild to moderate PS (N=13, P=0.005) but not in atopic dermatitis or healthy controls. However, in patients (N=6) requiring surgery for aneurysm, a predominance of Type 1 (IL-18R(+)) NKT lymphocytes over NKT2 was detected among infiltrating lymphocytes isolated from atherosclerotic plaques. Our data therefore demonstrate that ST2L and IL-18R could serve as important determinants of the immune status of human diseases.